IntroductionPosted by Will Stevens Sun, February 28, 2016 00:01:20The RepRap project has two parallel, overlapping aims - one is to make readily accessible low-cost 3D printers, the other is to make self-replicating 3D printers. The project was able to achieve the first goal because a RepRap is able to make many of its own mechanical parts: structural elements, gears, springs etc...

I'm interested in RepRap because I'm interested in self-replicating programmable constructors - i.e. machines that can be programmed to construct other machines, and which can construct themselves.

A difficulty in making a more completely self-replicating RepRap is the control system. RepRaps are controlled by microcontrollers, and microcontrollers are made by a complex process in expensive semiconductor fabrication plants.

I'm investigating whether a relay-based RepRap control system can be built using relays made from RepRapped parts, iron nails, and copper wire. My motivation for the project is largely curiosity about whether it can be done. I don't expect a RepRap controlled by relays to have any practical value. And if the project doesn't succeed, then finding out exactly why it won't work is almost as good as succeeding.

Some forum posts about some of the ideas involved in this project can be found here:

- A stepper motor speed and direction controller made from off-the-shelf relays.

- A 3D printed relay that seems to operate reliably for 10,000s of operations (when switching low-current non-inductive loads at a switching rate of 10 cycles per second).

- A circuit diagram for a simple RepRap controller made from about 50 relays and a punched card reader.

Further details about these will be posted in due course.

At the moment it seems to me that the biggest hurdle in this project is likely to be the reliability of RepRapped relays when switching inductive loads (the coils of other relays). In order to be able to start printing useful objects, all of the relays in the controller need to operate about 10000 times at a speed of at least 5Hz without any of them malfunctioning.